The present invention relates to a gripping arrangement in general, and more particularly to a gripping device for use in machines for treating elongated workpieces, such as draw benches, stripping machines and similar arrangements.
There are already known various gripping arrangements for use in drawing or stripping machines and, generally speaking, they include a plurality of jaw elements which sequentially close around the workpiece and advance the workpiece in a predetermined direction, thus drawing the workpiece through a die. Among the known gripping arrangements, there are already such in which two supports are guided on rails or similar guiding arrangements for reciprocation in the direction of advancement of the workpiece, which supports are equipped with jaw elements, such jaw elements being mounted on their respective supports for movement generally in the radial direction of the workpiece between a closed and an open position thereof so as to engage and disengage the workpiece.
Some of the important problems which have to be solved when drawing long or endless workpieces through a die or out of a treating machine are, on the one hand, to obtain high throughput of the drawing arrangement and of the gripping arrangement and, on the other hand, to obtain uniform drawing speed despite the fact that the drawing force is exercised upon the workpiece by one support and its associated jaw elements for part of the operating cycle, and by the other support and its associated jaw elements for another part of the cycle. A further requirement which must be satisfied in connection with each gripping or drawing arrangement is that it be simple, economical and reliable.
To solve the above problems and to satisfy the above requirements, it has been already proposed to provide a gripping arrangement for use in a drawing machine, which gripping or drawing arrangement includes only a single tensioning support which draws the workpiece through the die as it moves in one direction away from the die, whereas the tensioning support is returned to its initial position in the opposite direction at an increased speed in order to keep the intervening time periods between successive drawing operations to a minimum. It will be appreciated that this arrangement operates on an intermittent basis, which is not objectionable in some instances. Inasmuch as substantial forces are applied to and transmitted by the tensioning support to the workpiece being drawn, the tensioning support has usually substantial weight and, consequently, high inertia. The high inertia of the tensioning support determines the upper limit to the increase in the speed of return movement of the tensioning support. Thus, this type of an arrangement is not suited for many applications.
There are also already known many different constructions of gripping, tensioning and drawing arrangements which utilize caterpillar-like advancing arrangements in which the workpiece is gripped between jaws which are arranged on a pair of caterpillar-like conveyors which run at the same speed and also in the same direction in the region of engagement with the workpiece. It will be appreciated that this type of an arrangement is very complex and expensive, particularly because of the need for precise synchronization of the advancement of the two conveyors, and the need for providing the plurality of the gripping jaws on the two conveyors, which gripping jaws must be precisely machined to cooperate with one another, only less than a half of the gripping jaws being in engagement with the workpiece being drawn at any given moment.
In a further prior art construction, there is provided a drawing or gripping arrangement which includes two tensioning supports mounted for movement on guiding rails in such a manner that one of the tensioning supports is arranged behind the other tensioning support when viewed in the direction of advancement or drawing of the workpiece. Because of this successive arrangement of the two tensioning supports, each of the supports is capable of drawing the workpiece through a distance which approximately corresponds to half the length of the guiding rails, whereupon the other tensioning support takes over and the first tensioning support returns to its initial position, the same procedure being followed for the other tensioning support. This results in a drawing machine, or a gripping and drawing arrangement therefor, the guide rails of which are excessively long.